Liquid interface MCQs With Answer

Liquid interface MCQs With Answer is an essential study resource tailored for B.Pharm students studying interfacial phenomena in pharmaceutical formulations. This concise, SEO-friendly introduction highlights key concepts such as surface and interfacial tension, wetting, contact angle, surfactants, micellization, emulsification, and measurement techniques used in dosage form design. Understanding liquid interfaces helps in optimizing drug solubility, stability of emulsions and suspensions, transdermal and ocular formulations, and nanoparticle assembly. These MCQs emphasize both theory and practical applications, clarify measurement methods (pendant drop, Wilhelmy plate), and reinforce formulation strategies using surfactants and polymers. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What is surface tension?

• The force per unit length at a liquid surface
• The volume of liquid in contact with air
• The weight of a liquid column
• The electrical potential at the interface

Correct Answer: The force per unit length at a liquid surface

Q2. What are the SI units of surface or interfacial tension?

• Pascal-second (Pa·s)
• Newton per meter (N/m)
• Joules per mole (J/mol)
• Meter per second (m/s)

Correct Answer: Newton per meter (N/m)

Q3. Which molecular interaction primarily causes surface tension?

• Covalent bonding at the surface
• Electrostatic attraction to the container
• Cohesive forces between liquid molecules
• Gravitational attraction of the liquid molecules

Correct Answer: Cohesive forces between liquid molecules

Q4. What does the contact angle measure?

• The concentration of surfactant at the interface
• The angle between liquid surface and solid surface indicating wetting
• The viscosity change near the interface
• The electric charge of a droplet

Correct Answer: The angle between liquid surface and solid surface indicating wetting

Q5. Young’s equation relates which parameters?

• Surface tension, temperature, and viscosity
• Contact angle and interfacial tensions between solid, liquid, and gas
• CMC, HLB, and micelle radius
• Droplet volume and evaporation rate

Correct Answer: Contact angle and interfacial tensions between solid, liquid, and gas

Q6. A positive spreading coefficient (S > 0) indicates what?

• The liquid will partially bead on the surface
• The liquid will spread spontaneously over the substrate
• The surface will become hydrophobic
• The surfactant will precipitate

Correct Answer: The liquid will spread spontaneously over the substrate

Q7. Jurin’s law for capillary rise shows that rise height is inversely proportional to which parameter?

• Surface tension
• Contact angle
• Capillary radius
• Liquid density

Correct Answer: Capillary radius

Q8. What is the primary pharmaceutical role of surfactants at liquid interfaces?

• Increase melting point of APIs
• Decrease surface/interfacial tension and stabilize interfaces
• Act as preservatives only
• Prevent chemical reactions between excipients

Correct Answer: Decrease surface/interfacial tension and stabilize interfaces

Q9. The HLB (hydrophilic-lipophilic balance) value helps to:

• Predict melting behavior of polymers
• Choose suitable surfactants for oil-in-water or water-in-oil emulsions
• Determine drug pKa
• Measure particle charge

Correct Answer: Choose suitable surfactants for oil-in-water or water-in-oil emulsions

Q10. Critical micelle concentration (CMC) is defined as:

• The concentration where surfactants begin to hydrolyze
• The concentration above which micelles form in solution
• The concentration at which surface tension is maximum
• The point where surfactants precipitate

Correct Answer: The concentration above which micelles form in solution

Q11. Which method is commonly used to determine CMC experimentally?

• pH titration
• Surface tension versus log concentration plot
• High-performance liquid chromatography
• Mass spectrometry

Correct Answer: Surface tension versus log concentration plot

Q12. Micelle formation in solution primarily increases which property of poorly soluble drugs?

• Melting point
• Aqueous solubility via solubilization in micelle cores
• Vapor pressure
• Crystal lattice energy

Correct Answer: Aqueous solubility via solubilization in micelle cores

Q13. In emulsions, emulsifiers function mainly by:

• Increasing droplet viscosity
• Providing an interfacial barrier to prevent coalescence
• Removing water from the oil phase
• Promoting Ostwald ripening

Correct Answer: Providing an interfacial barrier to prevent coalescence

Q14. Zeta potential of droplets or particles indicates:

• Thermal stability of the formulation
• The electrostatic surface charge that affects colloidal stability
• The molecular weight distribution
• The hydrophobic chain length of surfactants

Correct Answer: The electrostatic surface charge that affects colloidal stability

Q15. Ostwald ripening in emulsions refers to:

• Droplet coalescence due to mechanical stress
• Growth of larger droplets at expense of smaller ones by diffusion
• Surface oxidation of droplets
• Formation of micelles from droplets

Correct Answer: Growth of larger droplets at expense of smaller ones by diffusion

Q16. Coalescence in emulsions is defined as:

• Reversible aggregation of droplets
• Permanently merging of two droplets into one larger droplet
• Evaporation of the dispersed phase
• Formation of a lamellar phase

Correct Answer: Permanently merging of two droplets into one larger droplet

Q17. Creaming of an emulsion is best described as:

• The chemical degradation of surfactant
• Upward migration of dispersed droplets due to density differences
• Irreversible flocculation
• The formation of microemulsions

Correct Answer: Upward migration of dispersed droplets due to density differences

Q18. Interfacial rheology measures:

• Viscoelastic properties of the interface
• Electrical conductivity of the bulk
• Melting point of lipids
• Optical density of emulsions

Correct Answer: Viscoelastic properties of the interface

Q19. The Marangoni effect causes fluid flow due to:

• Temperature or composition-driven surface tension gradients
• Magnetic fields acting on droplets
• Increase in bulk viscosity only
• Gravitational instabilities in the bulk

Correct Answer: Temperature or composition-driven surface tension gradients

Q20. Gibbs adsorption isotherm relates changes in surface tension to:

• Surface excess concentration of the solute at the interface
• Bulk viscosity changes
• Viscosity of the surfactant solution
• Contact angle hysteresis

Correct Answer: Surface excess concentration of the solute at the interface

Q21. The pendant drop method measures interfacial tension by:

• Analyzing the shape of a hanging drop
• Measuring the time for a droplet to evaporate
• Recording the color change at the interface
• Counting the number of formed micelles

Correct Answer: Analyzing the shape of a hanging drop

Q22. The Wilhelmy plate technique determines surface tension by measuring:

• The electrical resistance of a plate
• The force on a plate partially immersed at the interface
• The evaporation rate from a plate
• The refractive index near the surface

Correct Answer: The force on a plate partially immersed at the interface

Q23. The Du Noüy ring method is used to measure:

• Particle size distribution
• Surface or interfacial tension by pulling a ring from the surface
• Viscosity using capillary flow
• Thermal conductivity of liquids

Correct Answer: Surface or interfacial tension by pulling a ring from the surface

Q24. Why is contact angle important in transdermal formulation design?

• It indicates the drug’s pKa
• It predicts adherence and wetting of formulation on skin
• It measures the molecular weight of permeants
• It determines the emulsion color

Correct Answer: It predicts adherence and wetting of formulation on skin

Q25. In ocular drops, appropriate surface tension is crucial to:

• Enhance drug crystallinity
• Ensure proper spreading and comfort on the eye surface
• Increase container shelf life only
• Prevent microbial contamination solely

Correct Answer: Ensure proper spreading and comfort on the eye surface

Q26. Interfacial polymerization is commonly used to prepare:

• Immediate-release tablets
• Microcapsules and nanocapsules with polymer shells
• Uncoated lipid solutions
• Freeze-dried powders without shells

Correct Answer: Microcapsules and nanocapsules with polymer shells

Q27. Nanoemulsions often improve oral bioavailability because they:

• Increase droplet size to enhance absorption
• Provide small droplet size and large interfacial area for better dissolution
• Are thermodynamically unstable
• Eliminate the need for surfactants

Correct Answer: Provide small droplet size and large interfacial area for better dissolution

Q28. The critical packing parameter (CPP) of surfactants helps predict:

• The pH stability range of surfactants
• The likely self-assembled aggregate shape (micelle, vesicle, bilayer)
• The molecular weight distribution
• The ionic strength dependence of CMC

Correct Answer: The likely self-assembled aggregate shape (micelle, vesicle, bilayer)

Q29. Langmuir monolayer studies provide information about:

• Bulk solubility of surfactants only
• Molecular packing and phase behavior at the air-water interface
• The thermal degradation of polymers
• Electrical conductivity of monolayers

Correct Answer: Molecular packing and phase behavior at the air-water interface

Q30. Which of the following is a commonly used pharmaceutical surfactant?

• Polysorbate 80 (Tween 80)
• Sodium chloride
• Microcrystalline cellulose
• Talc powder

Correct Answer: Polysorbate 80 (Tween 80)

Q31. Adding electrolytes to ionic surfactant solutions typically:

• Increases CMC significantly
• Decreases CMC by screening head-group repulsion
• Has no effect on micellization
• Causes immediate precipitation of surfactant

Correct Answer: Decreases CMC by screening head-group repulsion

Q32. pH changes can affect ionizable surfactants by:

• Changing their color only
• Altering their ionization state and interfacial activity
• Turning them into polymers
• Eliminating van der Waals forces

Correct Answer: Altering their ionization state and interfacial activity

Q33. Which surfactant type is most sensitive to temperature via a cloud point?

• Anionic surfactants
• Cationic surfactants
• Nonionic surfactants
• Polymeric insoluble surfactants

Correct Answer: Nonionic surfactants

Q34. The cloud point of a nonionic surfactant is:

• The temperature at which the solution becomes turbid due to phase separation
• The pH at which surfactant ionizes
• The CMC multiplied by temperature
• The maximum surface tension achievable

Correct Answer: The temperature at which the solution becomes turbid due to phase separation

Q35. Improved wettability of a powder by lowering contact angle typically leads to:

• Slower dissolution rates
• Faster dissolution and better dispersion in aqueous media
• Increased tablet hardness only
• Reduced drug solubility

Correct Answer: Faster dissolution and better dispersion in aqueous media

Q36. Which approach is commonly used to reduce the contact angle of a solid powder?

• Coating with hydrophobic agents
• Surface modification with wetting agents or surfactants
• Decreasing particle size only
• Heating above melting point

Correct Answer: Surface modification with wetting agents or surfactants

Q37. Wicking in transdermal patches is governed by:

• Magnetic properties of the adhesive
• Capillary action and porous microstructure
• Bulk viscosity alone
• pH of the skin exclusively

Correct Answer: Capillary action and porous microstructure

Q38. Marangoni stresses are important in spray drying and coatings because they:

• Promote uniform film formation by counteracting thinning
• Always destabilize films causing defects
• Are irrelevant at micron scales
• Only affect thermal conductivity

Correct Answer: Promote uniform film formation by counteracting thinning

Q39. Interfacial tension plays a critical role in liposome formation by affecting:

• Lipid bilayer packing and vesicle size
• API chemical stability exclusively
• Color of the formulation
• Only the pH of the aqueous phase

Correct Answer: Lipid bilayer packing and vesicle size

Q40. The spreading coefficient S is given by S = γ_SG – (γ_SL + γ_LG). If S > 0, what happens?

• The liquid forms a spherical droplet
• The liquid spreads spontaneously over the solid
• The surfactant precipitates
• The contact angle increases above 90°

Correct Answer: The liquid spreads spontaneously over the solid

Q41. Tensiometry can provide information about:

• Surface/interfacial tension and adsorption kinetics
• Drug potency directly
• Only particle size of emulsions
• Colorfastness of coatings

Correct Answer: Surface/interfacial tension and adsorption kinetics

Q42. At an air-water interface, amphiphiles typically orient with:

• Hydrophilic heads toward air and tails into water
• Random orientation with no order
• Hydrophilic heads in water and hydrophobic tails toward air
• Both head and tail buried in bulk water

Correct Answer: Hydrophilic heads in water and hydrophobic tails toward air

Q43. DLVO theory combines which forces to explain colloidal stability?

• Only van der Waals attractions
• Electrostatic repulsion and van der Waals attraction
• Magnetic and gravitational forces
• Hydrogen bonding and covalent bonding

Correct Answer: Electrostatic repulsion and van der Waals attraction

Q44. Steric stabilization of colloids is achieved by:

• Adding small ionic surfactants only
• Adsorbing polymers or nonionic surfactants to create a physical barrier
• Increasing the temperature above boiling point
• Removing all surfactants

Correct Answer: Adsorbing polymers or nonionic surfactants to create a physical barrier

Q45. Which emulsification method uses high shear to reduce droplet size?

• Low-energy spontaneous emulsification
• High-pressure homogenization or high-shear mixing
• Freeze-thaw cycling only
• Simple stirring without shear elements

Correct Answer: High-pressure homogenization or high-shear mixing

Q46. Co-surfactants in microemulsions primarily serve to:

• Increase bulk viscosity
• Lower interfacial tension further and aid in flexible interfacial film formation
• Solidify the dispersed phase
• Reduce drug potency

Correct Answer: Lower interfacial tension further and aid in flexible interfacial film formation

Q47. A key difference between emulsions and microemulsions is:

• Microemulsions are thermodynamically stable while emulsions are typically kinetically stable
• Emulsions are always clear and isotropic
• Microemulsions cannot solubilize drugs
• Emulsions do not require surfactants

Correct Answer: Microemulsions are thermodynamically stable while emulsions are typically kinetically stable

Q48. Generally, how does temperature affect surface tension of liquids?

• Surface tension increases with temperature
• Surface tension decreases with increasing temperature
• Temperature has no effect
• Surface tension oscillates unpredictably with temperature

Correct Answer: Surface tension decreases with increasing temperature

Q49. Initial adsorption of surfactant molecules to a fresh interface is often controlled by:

• Diffusion of surfactant molecules to the interface
• Chemical reaction at the interface only
• Long-range gravitational settling
• Bulk crystallization rate

Correct Answer: Diffusion of surfactant molecules to the interface

Q50. Which instrument is commonly used to measure static contact angle?

• Spectrophotometer
• Contact angle goniometer
• Gas chromatograph
• Mass spectrometer

Correct Answer: Contact angle goniometer

G S Sachin

I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.

Mail- Sachin@pharmacyfreak.com